An infrared thermal imaging device uses an infrared detector and an image-forming optical lens to receive an energy distribution pattern of infrared radiation emitted by a detected target object, and reflects the received energy distribution pattern of infrared radiation to a light-sensitive element of the infrared detector, thus obtaining an infrared thermogram. The infrared thermogram corresponds to the thermal distribution of the object. In other words, the infrared thermal imaging device reflects invisible infrared energy emitted by the object as visible infrared thermograms. Different colors of the infrared thermogram represent different temperatures of the detected object. The infrared thermal imaging device displays the differences between the temperatures of the object, but when the surface temperature of the object is close to or equal to the ambient temperature, the object cannot be identified. Therefore, generally a visible light sensor would be attached to an advanced infrared thermal imaging device to assist the infrared thermal imaging device to identify the target object when the temperature differences are small.
Although the prior art can perform an image fusion enhancement using the visible light sensor, a visible image will still be superposed on the infrared thermogram when the infrared thermogram is relatively clear, which may cause loss of details of the infrared thermogram. In addition, it is necessary to continually manually adjust the fusion ratio in different scenes in order to accurately identify the target object when using conventional image fusion methods, which is complicated to operate, and requires operators to have enough professional knowledge, thus it is not conducive to the intelligence and popularity of the infrared thermal imaging device.